Construction for electrolytic cell



April 5, 1966 J. SZECHTMAN 9 5 CONSTRUCTION FOR ELECTROLYTIC CELLOriginal Filed Feb. 1'7, 1961 2 Sheets-Sheet l .INVENTOR. JOSHUASZECHTMAN ATTORNEY CONSTRUCTION FOR ELECTROLYTIC CELL Original FiledFeb. 17. 196i 2 sheets-sheet 2 INVEN TOR. JOSHUA SZECHTMAN ATTORNEYUnited States Patent 3,244,609 CONSTRUCTIQN FOR ELEQTROLYTIC CELL JoshuaSzechtman, Byram, C0nn., assignor to Chlormetals Incorporated, New York,N.Y., a corporation of Delaware Continuation of application Ser. No.89,943, Feb. 17, 1961. This application May 26, 1964, Ser. No. 377,162

6 Claims. (Cl. 294-219) This is a continuation of my co-pendingapplication Serial No. 89,943, filed February 17, 1961 now abandoned.

This invention relates to an electrolytic cell of the type involving amobile cathode which flows in relation to at least one fixed anode, andthe invention is more particularly concerned with the control oradjustment of the gap between the cathode and the anode.

In the electrolysis of alkali metal salts and alkaline earth metalsalts, use is made of electrolytic cells of the mobile cathode typewhich employ, as the cathode, a liquid metal Which flows across the soleof the cell. Electrolytic cells of the mercury-cathode type are wellknown and, in US. Patent No. 3,104,213 of September 17, 1963, I havedescribed a cell which is adapted to be operated with a moltenelectrolyte and which employs molten lead as the cathode. Themercury-cathode electrolytic cell is commonly employed for theelectrolysis of aqueous salt solutions, particularly sodium chloridebrine, and the liberated metal, e.g. sodium, combines with the mercuryto form an amalgam. In the cell of my above-mentioned patent, theliberated metal combines with the molten lead to form an alloy fromwhich the metal can be subsequently readily recovered, e.g. bydistillation. The anodes of electrolysis cells of the liquid-cathodetype are generally formed from graphite and are electrically connectedto a source of electrical current. In the most satisfactory commercialcells of the horizontal type, each graphite anode is in the form of ablock having a substantially planar lower surface which is disposed at apredetermined distance from the surface of the flowing cathode. Thisdistance is referred to as the anodecathode gap, and the voltage in thecell varies, of course, with the size of the gap. During normaloperation of the cell, each graphite anode is gradually worn away, andthis wear is generally localized at the lower surface of the anode.Since the flow of the cathode remains substantially constant, wearingaway of the lower surface of the anodes gradually increases theanode-cathode gap, and this increase in the size of the gap causes agradual increase in the voltage. A certain amount of voltage increasecan be tolerated but after it has reached a maximum practical value,which depends upon the particular cell, further increase in voltage mustbe prevented if economical operation of the cell is to be achieved.Accordingly, it has been customary to lower the anodes from time to timeto reduce the anode-cathode gap to the optimum distance, e.g. thedistance at which .each anode was originally set when new. While suchoperation does, of course, compensate for the wear of the anodes andkeeps the voltage within practicable operating limits, this method hascertain practical disadvantages. The graphite anodes have a stem orsupport extending upwardly through the cover plate of the cell and topermit the lowering of the anodes to compensate for wear, as justdescribed, it is necessary to provide for sliding movement of the anodestem in the cover plate. This makes necessary the provision of specialmeans which will permit the sliding movement and yet which will retainthe fluid-tightness of the cell. From a practical standpoint thispresents many problems and is not wholly satisfactory. Various otherproposals have been made to solve the problem of compensating for anodewear, but all suffer from one or more practical disadvantages andgenerally involve a complicated and expensive con struction.

It is an object of the present invention to provide an electrolytic cellwhich includes means for regulating and adjusting the anode-cathode gapwhich avoids the drawbacks and disadvantages enumerated above.

It is a further object of the invention to provide a method foradjusting the anode-cathode gap of a horizontal electrolytic cell of theliquid cathode type without requiring any shifting of the anodes.

In accordance with the invention, the anode-cathode gap of aliquid-cathode electrolytic cell is adjusted and maintained at theoptimum value by controlled regulation of the level of the flowingcathode stream in the cell. More particularly, there is provided, inaccordance with the invention, a cell construction having an outlet forthe liquid-cathode stream associated with means for selectivelypositioning the level at which the cathode flows into the outlet and,therefore, the level of the cathode stream flowing under the anodes inthe electrolysis chamber. More specifically, there is provided, inaccordance with the invention, an electrolytic cell of theliquid-cathode type in which the outlet is defined by a sleeve memberwhich is combined with vertical adjustment means for selectively raisingand lowering the sleeve in relation to the bottom of the cell.

It is a feature of the invention that the anode-cathode gap in anelectrolytic cell of the liquid-cathode type can be continuouslymaintained at any desired value without the necessity for moving theanodes in any way.

It is a further feature of the invention that maintenance of theanode-cathode gap at an optimum value can be achieved withoutinterrupting cell operation.

It is another feature of the invention that the control system providedby this invention for adjustment of the anode-cathode gap lends itselfreadily to completely automatic operation.

Other objects and features of the invention will be readily apparentfrom the following detailed description of an illustrative embodimentthereof and from the accompanying drawings wherein:

FIG. 1 is a longitudinal cross-sectional view of an electrolytic cellembodying features of the present invention; and

FIG. 2 is an enlarged view of the right-hand portion of FIG. 1 showingthe details of the construction of the cathode-level adjustingmechanism.

Referring to the drawings, there is illustrated an electrolytic celldesignated generally by the reference numeral 10. The cell body 12 ofthe cell 10 is suitably formed from metal, and is supported upon aninsulating support 14 indicated in the drawing as refractory blocks orbricks, but it will be understood that any other convenient insulatingbase may be employed. As seen in FIG. 1, the cell 10 defines a solesurface 15 upon which the liquid cathode 16, e.g. molten lead, isadapted to rest and to flow from left to right. Thus, the elongated cellbody 12 is formed with an elongated channel of which the sole 15 is thebottom and which provides the electrolysis chamber 17. The sole 15 maybe horizontal or it may slope slightly toward the right, the slope ofthe cell may vary but a slope of 1 or less is preferred. When the cellis adapted to be operated at elevated temperatures for the electrolysisof molten salts, e.g. temperatures of 810 to 850 C. which are suitablefor the electrolysis of molten sodium chloride, any convenient meansforheating the cell body and maintaining it at an elevated temperaturemay be employed. Actually, the electrolysis reaction is exothermic butthe heating means is provided in order to bring the cell to operatingtemperature and to minimize heat loss so that desired operatingtemperature is always maintained.

Closing the cell is a cover 30 which extends completely across the cellbody 12 and also extends from one end of the cell body to the other.This cover is formed from an electrically-conductive material and, mostsuitably, it is formed from graphite.

The cover 30 directly supports the anodes 50 and such support iseffected by means of anode stems 52. While in US. Patent No. 3,104,213 Ishow a conduit extending through the cover for the removal of chlorinegenerated in the cell during electrolysis, and a similar outlet is shownat 55 in FIG. 1, provision may be made for withdrawing chlorine from thecell through the anodes and through the cover in the manner described inFrench Patent No. 1,287,758.

The power connections are indicated diagrammatically at 56 and 57, butit will be understood that any conventional means may be employed toattach the power conductors, and a particularly suitable system is shownin said US. Patent No. 3,104,213. Similarly, the cover is suitablyelectrically insulated from the body of the cell since it is a conductorof electrolysis current. It is ad vantageously covered with heatinsulation, as shown in the drawing.

As seen in FIG. 1, the liquid cathode, e.g. molten lead, and theelectrolyte, e.g. molten alkali metal or alkaline earth metal salt, isintroduced at the left-hand end of the cell body, the molten leadsuitably being introduced through a conduit 80 and the electrolyte beingintroduced through a conduit 82. The conduit 82 extends upwardly intothe electrolysis chamber 17 and discharges through a self-regulatingfloat valve indicated diagrammatically at 84, of the type described inFIG. of U.S. Patent No. 3,104,213. At the right-hand end of the cellbody 10, there is provided at least one transverse Wall extendingbetween the side walls of the cell body and engaged by the cover 30 todefine the downstream end of the electrolysis chamber proper and todefine at least one end compartment. In the embodiment illustrated,there are shown two transverse walls 88 and 89 which define an endcompartment 90 and an intermediate compartment 92, the intermediatecompartment being provided with an outlet 94 for removal of dross whichmay accumulate upon the cathode and may be flushed out in the mannerdescribed in U.S. Patent No. 3,104,213. However, the second transversewall 89 may be omitted along with the outlet 94. The cell bottom slopesdownwardly in the vicinity of the transverse walls in order to formwells into which the transverse walls can extend to form liquid sealsagainst passage of the lighter electrolyte into the end compartments aslong as the liquid level of the cathode is maintained.

Since the principal desired product of the electrolysis reaction, i.e.the alkali metal or alkaline earth metal, is contained in the liquidcathode, means are provided for removing this fluid from the cell and,in accordance with this invention, means are provided to cooperate withthe cell outlet structure to permit accurate adjustment of the level ofthe liquid cathode in the cell.

As seen more particularly in FIG. 2, the end compartment 90 is providedwith an outlet defined by a cylindrical outlet conduit cylinder 102which is rotatably mounted in a sleeve 104 rigidly secured in the cellbottom. The cylinder 102 defines a seat 105 for reception of the lowertapered end of a cylindrical sleeve 106. The outlet cylinder 102 isformed with a thread 107 which cooperates with a corresponding thread108 in the sleeve 104 so that, upon rotation of the cylinder 102 withinthe sleeve 104, the cylinder will move axially in one direction or theother. The outlet cylinder 102 is hollow and discharges into an outletconduit 109, a suitable fitting 115 being provided between the conduit109 and the sleeve 104. In the drawing the outlet control mechanismdescribed above is exaggerated in size in order to facilitate theunderstanding of the invention. As seen in the drawing, portions of theabove-described construction extend below the level of the support 14and these portions may be disposed in a trough in the supporting surfaceor they may be formed so as to be accommodated within the support 14,which may have a greater height if desired.

Rotation of the outlet cylinder 102 to effect its axial displacementwithin the sleeve 104 is effected by any suitable means and, is shown inFIG. 2, an eflicient rotating mechanism comprises a shaft which extendsdownwardly through sleeve 106, and is connected at its lower end to theoutlet cylinder 102 by means of cross bars 122. The upper end of theshaft 120 extends through the cover of the end compartment and asuitable shaft seal provided by seal members 124 and 125 is provided toseal the opening through the cover. The upper end of the shaft 120 isprovided with a handle 127, suitably formed from electrically-insulatingmaterial, and a handlesecuring bracket 128, provided with a set screw130, is mounted adjacent the handle to facilitate the proper setting ofthe outlet cylinder 102. The set screw may be formed with a calibratedstern so that the exact position of the outlet cylinder can bedetermined.

The cylindrical sleeve 106 is formed with overflow apertures 132 and thelevel of the cathode in the cell is determined by the level of theseapertures. Consequently, when it is desired to raise the level of thecathode, it is merely necessary to raise the sleeve 106 and, conversely,when it is desired to lower the level of the cathode, such can beeffected by lowering the sleeve 106. It will be apparent that suchraising and lowering of the sleeve 106 is efiected by rotating outletcylinder 102 which supports the sleeve 106 and controls its axialposition. Consequently, when, in the course of operation of the cell,the,

anode-cathode gap increases due to wear of the anode faces, the gap canbe returned to its desired optimum value by raising the level of thecathode a corresponding amount. This is readily effected merely byraising the outlet cylinder 102 by rotating it in the appropriatedirecion within the sleeve 104. The thread between the outlet cylinder102 and the sleeve 104 has been exaggerated in the drawing to facilitateillustration and it can be of any desired form in order to make possibleany desired increments of movement upon each adjustment of the cathodelevel relatively to the faces of the anodes. There may be a slightleakage of lead alloy between the threads but this will be a very minoramount compared with the total outflow of lead alloy from the cell andsuch leakage is taken into account in forming the outflow apertures 132and in no way interferes with the operation or eifectiveness of thecathode-level control system.

As previously indicated, one of the advantages of the construction ofthis invention is the fact that it is readily adapted for automaticcontrol. Thus, since an increase in the anode-cathode gap causes avoltage increase, a relay can be readily connected to be actuated upon avoltage increase beyond a predetermined value and this. relay can inturn be connected to a reversible motor having a shaft connected to theshaft 120 of the level control mechanism. Thus, when the voltageincrease exceeds the predetermined value, the relay will be actuated tocause the motor to be energized and the cathode level will be raiseduntil the voltage increase has been nullified, at which time the motorwill be de-energized in response to the deactivation of the relay, andfurther adjustment will stop. This automatic regulating mechanism hasnot been illustrated but the manner in which it may be provided will bereadily apparent to a person skilled in the art. Such a system isparticularly effective in a cell operating for the electrolysis ofmolten salts and using a molten lead cathode as described.

There is thus provided an effective and accurate method and means foreffecting regulation or adjust-ment of the anode-cathode gap in anelectrolysis cell of the mobile cathode type which in no way relies uponmovement of the anodes. The significance of the needfor adjustment ofthe anode-cathode gap is apparent from the following.

A mercury cell with new graphite anodes adjusted to a level that willprovide a gap of A" may, for example, indicate on the voltmeter that theoperating voltage is 4.1. After the anodes wear away by the gap betweenthe anodes and the surface of the flowing cathode will increase to A butthen the voltage across the cell may jump to 4.2. Since it is notunusual for a mercury cell to have 30,000 amps applied to it, the energyloss due to the slightly increased gap will be 30,000 (4.24.1)=3000watts or 3 kw.

These cells operate continuously 24 hours a day and that means a powerloss of 72 kWh. per cell every day. A plant may have a hundred or moreof such cells operating and the total power loss may become enormous. Ihave mentioned only a small increase in the gap between anode andcathode, but as the cell continues in service, the gap will becomegreater and greater. So will the power losses.

It is, therefore, not surprising that many patents have been issued forinventions relating to the adjustment of anodes. The idea underlying allprior patents is to lower the anodes relatively to the cathode. A legionof ingenious devices have been developed to effect this operation.

While the method and apparatus of this invention are particularlysuitable for use in connection with the electrolysis of molten salts athigh temperatures in the presence of a molten lead cathode, it will beunderstood that the invention is also fully applicable tomercury-cathode cells.

Mercury is expensive and minor increases in the thickness of the mercuryfilm in a normal-sized cell will add several thousands of dollars worthof mercury to it. Further, mercury has poor Wetting qualities and theviscosity of mercury changes drastically in relation to the content ofsodium it absorbs. The situation is completely different when lead isused at the cathode. Its price is negligible by comparison and thewetting properties of lead are excellent and they are not aifected evenby relatively large quantities of absorbed sodium. However,mercury-cathode cells are becoming larger and larger. Cells operating on120,000 amps have already been built. Current densities applied tomercury cells are also increasing. Devices for lowering the anodes havebecome very involved and costly and, since the anodes must be adjustedfrequently, and in many cases individually, the labor involved isconsiderable. Mercurycathode cell operation will, therefore, benefitfrom this invention.

A further feature of this invention is that it may be combined withother cell-regulating mechanisms such as those described in US. PatentNo. 3,104,213. Normally the top of cylindrical sleeve 106 may be simplyreceived in a recess in the lower face of cover 30, the recess beingsufiiciently deep to accommodate the desired vertical movements of thesleeve, and suitably insulated to prevent electrical contact between thecover and the sleeve. To provide for other adjustment mechanisms,however, the cover 30 is provided with a suitably large aperture 140 topermit sleeve 106 to pass through and a graphite cap 141 having asuitably tall cylindrical portion 142 with a bottom integral flange 143is bolted or otherwise secured about the aperture 140.

The cap is provided with a top circular electromagnetic coil 145 and abottom circular electromagnetic coil 146 suitably spaced from coil 145in order not to interfere with it electromagnetically. The top of sleeve106 is provided with a weighted plug 147 secured within the sleeve, asby welding. A circular collar 148, subject to magnetic attraction, issecured to the sleeve 106 at a point suitable for attraction by theelectromagnet 6 when the latter is energized. A ring 149 is slidablydisposed about sleeve 106 so that it rests on sleeve lugs 150. The lugs150 keep ring 149 suitably above the surface of the end compartment.

The ring 149 is normally disposed below apertures 132 but may be raisedto close apertures 132, as will be described. The ring 149 is secured toupright standards 151 and the tops of standards 151 are secured togetherby a metal ring 152 subject to magnetic attraction. The ring 152 is alsoof suflicient weight to keep lower ring 149 below the level of theliquid cathode.

In order to clean dross from the cell, the sleeve 106 is rapidly liftedby energizing the electromagnetic coil 145, which attracts sleeve ring148, thereby lifting sleeve 106 and the slidable ring 149 disposed onthe sleeve lugs 150. This lifting of the sleeve 106 interrupts thenormal flow of liquid cathode through apertures 132 and instead permitsa relatively more rapid flow of cathode lead into outlet cylinder 102.The cathode level drops in the electrolysis chamber as well as in thechamber located between transverse walls 88 and 89 thereby permittingpassage of the molten floating salt and the dross thereon undertransverse wall 88. The molten salt with the dross thus pass into thechamber having the outlet 94. Release of the energizing action, actingon the top electromagnetic coil, causes the weighted sleeve to fall andcover the outlet aperture. This causes the level of the dross and moltensalt to rise in the chamber between the transverse walls and to pass outof the outlet 94.

When it is desirable t clean the bottom surface of the anodes, the cellcurrent is turned off and the bottom electromagnet is energized. Thiscauses the slide ring to rise and cover the sleeve apertures 132. Theresult is that the liquid level of the cathode rises to touch and washthe undersur'faces of the anodes in the cell. In operation, the anodesbecome fouled due to sulfur dioxide formation thereon, encrustations dueto foreign mater in the salt, etc. The flow of the cathode, particularlyin the case of lead, against these gaseous inclusions and leleteriousdeposits cleans the anodes.

After the liquid cathode has cleaned the anode undersurfaces, theenergizing action on the lower electromagnet is released and the ringfalls downwardly to its normal position on lugs 150 of the sleeve,thereby uncovering sleeve apertures 132 to permit resumption of normaloperation. The cell current is then turned on and the operation of thecell is resumed with the cleaned anodes. It will, of course, beappreciated that the anode cleaning mechanism above-described can beeliminated and that the anodes can be similarly cleaned by raising thecathode level by rotating cylinder 102 to a sufiicient extent.

It will be understood that various changes and modifications in additionto those indicated above may be made in the embodiments herein describedand shown in the drawings Without departing from the scope of theinvention as defined in the appended claims. It is intended, therefore,that all matter contained in the foregoing description and in thedrawings shall be interpreted as illustrative only and not as limitativeof the invention.

I claim:

1. A horizontal electrolytic cell of the liquid cathode type having anelectrolysis chamber including a bottom and at least one dependinganode, said depending anode being fixedly supported and held in relationto said bottom, and wherein the cathode flows over said bottom and undersaid anode and underlies the electrolyte with the surface of saidcathode being above the upper surface of said bottom, means foradjusting the anode-cathode gap in said chamber comprising a verticallyadjustable means for varying the level of said liquid cathode inrelation to said anode, said adjustable means being effective tomaintain the level of said liquid cathode above the level of said bottomin said electrolysis chamber and including a perforated overflow sleevemember slidably mounted in said chamber in sealing engagement with thebottom of said chamber, said sleeve member having an internal passagecommunicating with the exterior of said chamber, means threadablysecured in said chamber for vertically adjusting said sleeve member withrespect to said chamber and means'for mo'ving'said sleeve member out ofsealing engagement with the bottom of said chamber whereby liquidcathode can be conducted to the exterior of said chamber independentlyof the internal passage in said sleeve member.

2. A horizontal electrolytic cell of the liquid cathode type having anelectrolysis chamber including a bottom and at least one dependinganode, said depending anode being fixedly supported and held in relationto said bottom, and wherein the cathode. flows over said bottom andunder said anode and underlies the electrolyte with the surface of saidcathode being above the upper surface of said bottom, means foradjusting the anodecathode gap in said chamber comprising a verticallyadjustable means for varying the level of said liquid cathode inrelation to said anode, said vertically adjustable means including aperforated overflow sleeve mounted within said chamber on a rotatablehollow cylinder means, said cylinder means being rotatably mounted insaid bottom and vertically adjustable with respect to. said chamber uponrotation thereof.

3. A horizontal electrolytic cell as set forth in claim 2, wherein saidcylinder means and said bottom are formed with cooperating thread meansfor vertically ad.-

justing said cylinder means with respect to said bottom.

4. A horizontal electrolytic cell as set forth in claim 2 which furthercomprises a rotating mechanism connected to said rotatable cylinder forrotating said cylinder relative to said bottom, said mechanism extendingvertically upwardly to the exterior of said cell.

5. A horizontal electrolytic cell as set forth in claim 2,. wherein saidchamber is provided with means for raising: said perforated overflowsleeve independently of said rotatable cylinder means for draining thecathode directly through said rotatable cylinder means.

6. A horizontal electrolytic cell as set forth in claim 5 wherein saidraising means comprises cooperating electromagnetic means.

References Cited by. the Examiner JOHN H. MACK, Primary Examiner.

WINSTON A. DOUGLAS, Examiner.

1. A HORIZONTAL ELECTROLYTIC CELL OF THE LIQUID CATHODE TYPE HAVING ANELECTROLYSIS CHAMBER INCLUDING A BOTTOM AND AT LEAST ONE DEPENDINGANODE, SAID DEPENDING ANODE BEING FIXEDLY SUPPORTED AND HELD IN RELATIONTO SAID BOTTOM, AND WHEREIN THE CATHODE FLOWS OVER SAID BOTTOM AND UNDERSAID ANODE AND UNDERLIES THE ELECTROLYTE WITH THE SURFACE OF SAIDCATHODE BEING ABOVE THE UPPER SURFACE OF SAID BOTTOM, MEANS FORADJUSTING THE ANODE-CATHODE GAP IN SAID CHAMBER COMPRISING A VERTICALLYADJUSTABLE MEANS FOR VARYING THE LEVEL OF SAID LIQUID CATHODE INRELATION TO SAID ANODE, SAID ADJUSTABLE MEANS BEING EFFECTIVE TOMAINTAIN THE LEVEL OF SAID LIQUID CATHODE ABOVE THE LEVEL OF SAID BOTTOMIS SAID ELECTROLYSIS CHAMBER AND INCLUDING A PERFORATED OVERFLOW SLEEVEMEMBER SLIDABLY MOUNTED IN SAID CHAMBER IN SEALING ENGAGEMENT WITH THEBOTTOM OF SAID CHAMBER, SAID SLEEVE MEMBER HAVING AN INTERNAL PASSAGECOMMUNICATING WITH THE EXTERIOR OF SAID CHAMBER, MEANS THREADABLYSECURED IN SAID CHAMBER FOR VERTICALLY ADJUSTING SAID SLEEVE MEMBER WITHRESPECT TO SAID CHAMBER AND MEANS FOR MOVING SAID SLEEVE MEMBER OUT OFSEALING ENGAGEMENT WITH THE BOTTOM OF SAID CHAMBER WHEREBY LIQUIDCATHODE CAN BE CONDUCTED TO THE EXTERIOR OF SAID CHAMBER INDEPENDENTLYOF THE INTERNAL PASSAGE IN SAID SLEEVE MEMBER.